The present invention relates to fluid controllers of the type used to control the flow of fluid from a source of presurized fluid to a fluid pressure operated device such as a steering cylinder.
A typical fluid controller of the type to which the present invention relates includes a housing which defines various fluid ports, and further includes a fluid meter, valving and an arrangement for imperting follow-up movement to the valving in accordance with the flow through the fluid meter. The flow through the controller valving is directly proportional to the area of the main variable flow control orifice, which, in turn, is proportional to the rate at which the steering wheel is rotated.
Fluid controllers of the type to which the invention relates are frequently used on large, heavy vehicles. More particularly, such controllers are frequently used on articulated vehicles which have high inertia loads on the opposite side of the wheels from the pivot joint. The weight of such vehicles, and the inertia loads have made it difficult to achieve smooth steering action, and as a result, it has become common practice on such vehicles to provide a cushion valve in the lines interconnecting the fluid controller and the steering cylinder, although an accumulator could be used instead.
The use of an accumulator in the circuit has normally resulted in satisfactory performance, but the accumulator adds substantial expense to the cost of the system and requires a substantial amount of additional maintenance. On the other hand, a cushion valve, such as the type shown in U.S. Pat. No. 4,040,439, assigned to the assignee of the present invention, provides generally satisfactory cushioning of a first pressure spike, but not of immediately successive spikes. In addition, a typical cushion valve adds very substantially to the cost of the system.